Answer:
The proportion of this group that likes chocolate is 0.625.
Step-by-step explanation:
Conditional Probability
We use the conditional probability formula to solve this question. It is

In which
P(B|A) is the probability of event B happening, given that A happened.
is the probability of both A and B happening.
P(A) is the probability of A happening.
In this question:
Event A: Likes sprinkles
Event B: Likes chocolate
25% of your friends who like Chocolate (C) also like sprinkles (S).
This means that 
40% of your friends like sprinkles (S) topping.
This means that 
Of the friends who like sprinkles, what proportion of this group likes chocolate

The proportion of this group that likes chocolate is 0.625.